Many systems and products in industry and research are subject to high requirements regarding their leaktightness. These requirements depend on the type of leak, the leak rate or size of the leak which leak detection method is applied, respectively, which leak detection instrument is employed.
In the instance of test samples or subassemblies manufactured in the refrigerating industry, automotive industry or other industries, the method of sniffer leak detection is frequently employed. This method requires that the test sample or subassembly contains a test gas, preferably at an overpressure. Frequently, helium is employed as the test gas which before sealing off is introduced into the hollow spaces which are to be analysed for the presence of leaks. It is also known to employ gases present in any case within the test samples or subassemblies as the test gas, for example, SF6 or halogen gases in the refrigerating industry.
The test sample which is to be analyzed for the presence of leaks is scanned with the aid of the suction intake (tip) of a sniffer gun, which takes in test gas flowing out of a possibly present leak and which supplies said lest gas to a test gas detector. The test gas detector may be accommodated together with other components in an instrument to which the sniffer gun is connected, among other things, by means of a hose. Provided the detector is sufficiently small (for example, an infrared gas analyser), it may also be accommodated in the sniffer gun itself, thereby significantly reducing the response time.
Test gas leak detection instruments need to be calibrated frequently. To this end, it is known to employ reference leakage devices exhibiting a defined leak. Reference leakage devices for these purposes comprise a gas reservoir and a constriction having a known conductance. For the purpose of calibrating a leak detection instrument equipped with a sniffer gun, commonly the sniffer tip is located in the vicinity of the constriction and the leak rate indication is aligned. From the German patent application publications 27 02 002, 32 43 752 and 199 63 073, reference leakage devices of this kind are known.
Reference leakage devices shall exhibit, on the one hand, a constant gas flow over a period of time which is as long as possible (significantly longer than one year). On the other hand, if they are to be accommodated within the enclosure of a leak detection instrument, they need to be sufficiently small in size. This requires that the test gas be present under a high-pressure (8 bar and more) within the reference leakage device. Reference leakage devices of this kind are temperature sensitive. This applies in particular when the test gas assumes the liquid state at the pressures stated. For safety reasons, a maximum temperature must not be exceeded. Installing, for reasons of operational convenience, a reference leakage device of this kind within a leak detection instrument containing heat producing components is problematic, frequently even impossible.
During the calibration process employing an external reference leakage device it is required in the instance of the leak detectors employed to date, to start the calibration through a menu entry and confirm the process of “Sniff leak”/“Sniff air”. This is rather cumbersome and contradicts the idea of an instrument which is easy to operate. This applies above all to—frequently unskilled—persons who need to analyse items moving on a conveyor as to the presence of leaks using a sniffer gun. They cannot bother themselves as to an operation-wise cumbersome and therefore time-consuming calibration process.